Environmental Engineering Reference
In-Depth Information
Pure water is an excellent insulator but hard to ind in this condition in nature. Water in
nature is almost never completely free of ions; the smallest impurity, even at parts per tril-
lion (ppt), will make water electrically conductive. Water has a high dielectric constant. This
constant shows that its ability to make electrostatic bonds with other molecules is high,
meaning it can eliminate the attraction of the opposite charges of the surrounding ions.
Water is also a good solvent owing to its polarity. The ability of a substance to dissolve
in water is determined by whether the substance can match the strong attractive forces that
water molecules generate between other water molecules. If a substance has such prop-
erties that do not allow it to overcome these strong intermolecular forces, the molecules
are “pushed away” from the water and do not readily dissolve. Contrary to the common
misconception, water and hydrophobic substances do not “repel,” and the hydration of a
hydrophobic surface is energetically, but not entropically, favorable.
When an ionic or polar compound enters water, it is surrounded by water molecules
(hydration). The relatively small size of water molecules typically allows many water mol-
ecules to surround one molecule of solute. The partially negative dipole ends of the water
are attracted to positively charged components of the solute, and vice versa for the positive
dipole ends. In general, ionic and polar substances such as acids, alcohols, and salts are
relatively soluble in water, and nonpolar substances such as fats and oils are not. Nonpolar
molecules stay together in water because it is energetically more favorable for the water
molecules to hydrogen bond to each other than to engage in van der Waals interactions
with nonpolar molecules.
At ambient conditions, and at standard temperature and pressure of 25°C and 1 atm
(STP), water can behave more like a gel and possibly be capable of producing work, or
even storing information such as at the conditions observed at the boundary interfaces
identiied as Exclusion Zones (EZ), as proposed by Pollack [2] based on the detailed work
on photocatalytic surface boundary layers. He has been using substrates coated with TiO
2
,
gels, and naion, having properties known as superhydrophilic (extreme water loving), in
which water itself does not behave in anything resembling the expected way we thought
it should, or with substrates on the extreme opposite end of the scale in superhydrophobic
surfaces (extreme water loathing), when water can maintain perfectly its spherical shape
of a drop or the least amount of volume required to hold its mass, even loating on another
drop of water itself.
Pollack has noted the following changes of water properties within the EZ between the
hydrophilic substrate and the water boundary layers:
• Increased density
• Stabilizing by the organized stacking of the hexagonal molecules
• Reorientation of the dipoles
• Adding charge potential between the EZ and water adjacent to it
• Increasing viscosity
• Decreasing its latent heat
• Increasing its optical index of refraction
• Allowing the water molecule to exclude solutes
• Making the water molecule become nondipolar
In biological cells and small organisms, water is in contact with membrane and protein
surfaces that are hydrophilic; that is, these are surfaces that have a strong attraction to